Preparation And Properties Of Photo-anodes Of Dye-sensitized Solar Cell

Dye-sensitized solar cell (DSSC) is a new type of photoelectric energy conversion device with low cost, simple preparation procedure, stable photo-to-electric performance and friendly environment action, which make it have a good prospect of development and application,and has attracted worldwide attention. Since the M Gratzel research team reported highly efficient(～11%)dye-sensitized solar cell, DSSC has become the most promising alternative to conventional silicon solar cell. The photo-anode, a nanocrystalline thin film electrode with sensitizers, is the vital part of DSSC, which play an important role not only in absorbing sunlight and generating photoelectrons, but also in transmitting and collecting electrons, whose performance is directly related to the efficiency of DSSC. So there is very important significance in the research of photo-anodes of DSSC. In this thesis, according to some hot and difficult questions of photo-anode research, the ZnO and Zn2TiO4 electrode material were researched, natural dyes in the DSSC were discussed, and some new methods of improving photon-to-electric efficiency were raised for further research work.1. In our experiment,we used zinc acetate dihydrate (CH3COO)2 Zn·2H2O and mono-ethanolammine NH2CH2CH2OH as raw materials, successfully prepared Nanocrystalline ZnO porous thin film on the FTO conductive glass substrate by sol-gel method and spin coating method. The crystal structure and surface morphology of ZnO porous thin film were characterized by XRD and SEM, the results showed that nanocrystalline ZnO film electrode sintered at 450℃had good crystalline, ZnO particle size of about 30nm, and a rough and porous surface, which illustrated nanocrystalline ZnO film had great surface area and was able to be adsorbed more sensitizer.So nanocrystalline ZnO film electrode could be applicable to DSSC.Using phthalocyaninatozinc(ZnPc) dye and PbS quantum dots as sensitizers of nanocrystalline ZnO thin film electrodes, photo-anodes of ZnO were prepared and were characterized their optical absorption characteristics by measuring UV-vis spectra.The results showed that ZnPc dye and PbS quantum dots could well sensitize ZnO thin film electrodes, and the effect of ZnPc dye and PbS quantum dots composite sensitization was optimal. And then, a ZnO solar cell device utilizing nanostructured ZnO/Q-PbS/ZnPc film electrode as photo-anode was fabricated and tested its working characteristic curve. In simulation sunlight, a fill factor of 0.348, a schort-circuit photocurrent of 1.42mA, an open-circuit voltage of 304mV, and a overall light to electricity conversion efficiency of 0.696% for this solar cell device were obtained, which showed that the ZnO solar cell had a strong electro-optical response. If pore distribution, pore size and thickness of of the nano-crystalline ZnO porous film, material and preparation technics of counter electrode, composition of electrolyte and so on, should be optimized, the light to electricity conversion efficiency of the ZnO solar cell could be improved.2. Using zinc acetate dihydrate (CH3COO)2Zn·2H2O and tetrabutyl titanate [CH3(CH2)3O]4Ti as raw materials, we prepared nanocrystalline Zn2TiO4 samples by sol-gel method. And nanocrystalline Zn2TiO4 material was applied to DSSC electrode for the first time, which obtained encouraging results.TiO2 colloid solution and ZnO colloid solution were prepared by sol-gel method, and then were mixed up to precursor colloid solution of Zn2TiO4 by Zn and Ti molar ratio of 2:1.We successfully prepared Nanocrystalline Zn2TiO4 thin film on the FTO conductive glass substrate by sol-gel method and spin coating method. The surface morphology of Zn2TiO4 thin film sintered at 550℃was aracterized by SEM, the result showed that the Zn2TiO4 grains were basicly spherical or nearly spherical particles, well dispersed and no agglomeration phenomenon, and particle size of several nanometers.And the film surface was smooth and compact.Using phthalocyaninatozinc(ZnPc) dye and PbS quantum dots as sensitizers of nanocrystalline Zn2TiO4 thin film electrodes, photo-anodes of Zn2TiO4 were prepared and were characterized their optical absorption characteristics by measuring UV-vis spectra.The results showed that ZnPc dye and PbS quantum dots could well sensitize Zn2TiO4 thin film electrodes, and the effect of ZnPc dye and PbS quantum dots composite sensitization was optimal, which could greatly increase light absorption intensity.This paper first reported the Zn2TiO4 solar cell utilizing nanostructured Zn2TiO4/Q-PbS/ZnPc film electrode as photo-anode and its working characteristic. In simulation sunlight, the cell had a strong electro-optical response. In addition, encouraging results were obtained, achieving a fill factor of 0.409, a schort-circuit photocurrent of 1.38mA, an open-circuit voltage of 325mV, and a overall light to electricity conversion efficiency of 0.85%, which indicated that the Zn2TiO4 solar cell research has a good prospect of development and great significance. As the lack of experience and experimental conditions, the mechanism of the cell was not explored, which would be further studied.3. In order to replace the rare and expensive artificial dyes and synthetic inorganic compounds, we tried to extract pigments from some fruits, flowers, leaves of natural vegetation and then employed in DSSCs.Testing their performance, we wanted to explore the performance of the natural dyes as sensitizers of DSSC.The seven kinds of natural dyes were extracted from flowers, leaves, and fruits, and were measured their optical absorption characteristics by using UV-vis photometer. By comparison, it was found that the natural dye extracted from leaves of Chinese rose showed better performance of the light response. Using the natural dye extracted from leaves of Chinese rose as sensitizers, the natural dye sensitized Zn2TiO4 electrode was prepared, and the natural dye sensitized Zn2TiO4 solar cell device was fabricated. The absorption spectra of the sensitized electrode was characterized by Uv-2550 spectrophotometer, the result showed that the UV-Vis absorption bands of the adsorbed dyes onto Zn2TiO4 film are broadened and the corresponding maxima are red shifted with respect to its solution, and the natural dye presented a little ability of electron transfer and could well sensitize Zn2TiO4 film electrode. Current potential curve for the natural dye sensitized solar cell was tested under simulation sunlight, encouraging results were obtained with the extract of leaves of Chinese rose, achieving an open-circuit voltage of 94.5mV, a short-circuit photocurrent of 11.5μA, a fill factor of 0.285 and a maximum power output of 0.309μW. Obviously, the natural dye showed sensitization activity lower than synthetic ones. Actually, application of natural dye is far below the industrial requirements. Nevertheless, their study is a significant multi-disciplinary practice, which is useful for disseminating knowledge to educate people on renewable energy sources and supplied a new way that prepared low cost, environmentally friendly dye-sensitized solar cells. Our results are encouraging, yet, if the natural dyes would be separated and purified, the structure of cell would be further optimized and so on, the light to electricity conversion efficiency of the natural dye-sensitized solar cell will be improved.